A variety of different hydraulic control systems have been proposed for use with articulated arm devices such as excavators and the like.
Canadian patent 851,502 issued to Witwer on Sept. 15, 1970 discloses a excavator control system with remote controlled valves for diverting flow of hydraulic fluid in the system to selectively apply speed and power assist to selected of the hydraulic actuators.
Canadian patent 885,292 issued Nov. 9, 1971 to Caywood et al employs overload sensing devices in the hydraulic circuit to automatically decrease the forces applied when the overload circuits are activated.
It has also been proposed to use attitude controls for an implement mounted on an articulated arm, see for example Canadian paten 1,072,324 issued Feb. 26, 1980 and 1,076,795 issued May 6, 1980 both to Willard. These patents relate to a excavator type implement wherein the attitude of the bucket for example is maintained constant as the arm is manipulated.
Canadian patent 1,203,309 issued Feb. 15, 1986 to Saulters et al provides a computer control system for controlling the orientation of an articulated boom wherein an input signal defines a desired position and the arms are moved until the desired position and actual position substantially coincide. This is done by continuously comparing the actual sensed position of the arm and comparing the sensed with the desired position and continuing the movement until the two are substantially the same.
In the operation of this type of equipment particularly equipment where one segment of the arm (the boom) is significantly more difficult to move than another (the stick) the signal specifying movement in a particular direction may lead the actual movement of the segment and if the lead becomes excessive the control becomes erratic.